This invention relates to a ball game racket, more particularly intended for tennis, this racket being provided with a device for damping vibrations.
The playing qualities of a racket are determined by a rather large number of criteria which, in general, can be classified into two categories:
performance criteria: efficiency, snappiness, stiffness, etc. PA1 criteria of comfort for the player: gentleness, handling ability, etc. PA1 three located in a direction perpendicular to the plane of the racket; they are the simple bending modes perpendicular to the median longitudinal plane of the racket; PA1 two located in the plane of the racket; they are the lateral bending modes; and PA1 two others which are couplings between vibrations of bending perpendicular to the median longitudinal plane of the racket and of twisting relative to its median longitudinal axis.
However, some criteria, for example tolerance of off-centering of the ball impact, can fall into both categories.
These two categories of criteria are most often contradictory, so that, most of the time, comfort can be improved only at the expense of performance and vice versa.
It is known that a system subjected to a disturbance vibrates around one or more proper frequencies which are characteristic of the structure and result from its distribution of mass and stiffness. The behavior resulting from this set of vibrations is the sum of the displacements which are generated, in various directions, by the resonance frequencies of this structure. These displacements are minimal at the spots currently called vibration "nodes" and maximum at the spots currently called vibration "antinodes."
This vibratory behavior would be infinite in the absence of any damping property of the structure. In a general way, any physical system is subjected to one or more types of damping as long as energy is dispersed either by friction or by other dissipating systems, for example viscoelastic or hysteresis systems.
It was noted that in the case of the tennis player, the vibrations which are transmitted to him by his racket after impact of the ball are directly correlated with his perception of the behavior of his device. In the range of frequencies going from 0 to 1000 Hz, a range in which man is greatly receptive to the vibrations, tennis rackets vibrate in several directions and frequencies, which correspond to what will be called below "proper vibratory modes." It was possible to show seven proper vibratory modes closely correlated with the behavior of the racket in play:
By way of illustration, some of these vibratory modes are represented diagrammatically on the accompanying drawings in FIGS. 1-5.
The proper vibratory modes on which it is most important to act are, of course, the modes of greater energy, i.e., those that generate considerable deformations of the structure.
Therefore, it is advisable as a matter of priority to influence the three first modes of bending which are perpendicular to the plane of the racket, the two first modes of bending which are in the plane of the racket, as well as the first mode of coupling of the vibrations of bending which are perpendicular to the plane of the racket and twisting relative to its longitudinal axis.
It is already known, to adjust the playing qualities, to provide on the tennis racket relatively complex means to damp the vibrations. Thus it is known to add damping elements, which are relatively complex and bulky, at selected spots on the racket frame.